1. Field of the Invention
This invention relates to a signal processor, and more particularly to a signal processor which is suitable for processing musical tone signals.
2. Prior Art
Conventionally, a DSP (digital signal processor) formed of a stored program-type LSI is used to process musical tone signals. This type of DSP stores a desired microprogram into a microprogram register to carry out various kinds of signal processing according to the microprogram. According to the conventional DSP, the number of steps of the microprogram and the number of steps carried out in one sampling repetition period for signal processing are made equal to each other such that the microprogram is executed once per sampling repetition period. Such a signal processing method is advantageous in having a versatility that the DSP can be used for carrying out various programs ranging from one having a small size to one having a large size.
Further, due to recent progress in the LSI technology, more and more steps can be executed in one sampling repetition period. This makes it possible to carry out a program which is so complicated as was impossible to carry out, as well as to carry out a plurality of programs in parallel with each other.
However, in the conventional DSP, an increase in the number of steps that can be executed in one sampling repetition period brings about an increase in the storage area of the microprogram register, resulting in an increase in the total size of a LSI used therein. This leads to an undesired increase in the manufacturing cost.
Further, an increase in the number of steps that can be executed in one sampling repetition period, i.e. an increase in the number of steps of a program to be stored in the microprogram register is inevitable when it is required to carry out a complicated program which requires execution of the maximum number of steps that can be stored in the microprogram register. However, conventionally, it has also been required to prepare and store a plurality of programs or routines of the same kind into the microprogram register, when it is required to carry out the same processing, based on different kinds of input data, or to carry out the same processing, for a plurality of channels with the DSP being used as part of a tone generator.